feat(FN-2339): add configurable ntfy server support

- Add ntfy base URL to global settings schema/types with persistence coverage and regression tests
- Extend dashboard settings API/routes and Settings modal UI to edit and save a custom ntfy server
- Update notifier runtime to use configured ntfy base URL when sending notifications
- Document the new setting and include a changeset for @runfusion/fusion

packages/core/src/settings-schema.ts

@@ -21,6 +21,7 @@ export const DEFAULT_GLOBAL_SETTINGS = {
   defaultThinkingLevel: undefined,
   ntfyEnabled: false,
   ntfyTopic: undefined,
+  ntfyBaseUrl: undefined,
   ntfyEvents: ["in-review", "merged", "failed", "awaiting-approval", "awaiting-user-review", "planning-awaiting-input"],
   ntfyDashboardHost: undefined,
   defaultProjectId: undefined,